JP5111216B2 - Image recording apparatus and image recording method - Google Patents

Description

  The present invention relates to the field of ink jet recording in which an image is formed on a recording medium by an ink jet recording method. More specifically, the present invention relates to an image recording apparatus and image recording for recording an image by correcting density unevenness caused by recording characteristics of a recording element It is about the method.

As a method for recording an image on a recording medium, there is an ink jet recording method in which an ink droplet is ejected from an ink jet head to form an image.
In this ink jet recording method, ink droplets are ejected from a plurality of ejection openings, resulting from the recording characteristics (landing position error, variation in the amount of dropped ink liquid, etc.) for each recording element having ejection openings in the image to be recorded. There is a problem that uneven density occurs. This problem is particularly problematic in a single-pass inkjet system in which an image is recorded on the entire surface of a recording medium by fixing a line-type inkjet head and transporting the recording medium once in one direction.

As a method for correcting this density unevenness, a method for correcting density unevenness by changing the ejection driving conditions according to the density unevenness for each recording element and adjusting the dot diameter and dot density, and the density unevenness are adjusted. There is a method of correcting the image data to eliminate the influence of density unevenness on the recorded image.
Since the method of changing the ejection driving condition is to change the ink droplets ejected from the inkjet head, there are limitations on the driving method and the correction width of the inkjet head during implementation. On the other hand, in the method of correcting the image data in accordance with the density unevenness, the ink droplets actually ejected from the inkjet head are changed as they are, that is, the inkjet head itself is changed (that is, physically changed). However, since this can be realized by correcting the data, there is an advantage that the degree of freedom is high.

  Japanese Patent Application Laid-Open No. 2004-228688 discloses an image forming apparatus that forms an image by moving a recording head in which a plurality of recording elements are arranged relative to a recording medium in a direction different from the arrangement direction of the recording heads. A first correction unit that selectively indicates the recording characteristics of each element for each of a plurality of density regions, and a second correction that corrects the density signal based on the recording characteristics specified by the first correction unit. And an image forming apparatus comprising: a selecting unit that selects a recording characteristic instructed by the first correcting unit according to a density region to which a density signal corresponding to each recording element belongs. Yes.

Japanese Patent No. 2942048

  As described in Patent Document 1, a density correction curve (recording characteristic) common to recording elements having similar characteristics and a correction table (selection means) indicating which density correction curve each recording element corresponds to ) And determining the density correction curve using the correction table, the data amount can be reduced and the calculation amount can be reduced as compared with the case where the density correction curve is provided for each recording element.

Here, in the ink jet recording method, a non-ejection nozzle that does not eject ink droplets may occur. When this non-ejection nozzle occurs, a non-ejection correction coefficient value for adjusting the ejection amount of the nozzle near the non-ejection nozzle is calculated, and the non-ejection correction coefficient value is used to eject from the nozzle near the non-ejection nozzle. By adjusting the liquid droplets to be discharged, the influence of the non-ejection nozzle can be reduced.
The non-ejecting nozzle suddenly occurs due to dust clogging or the like, or the non-ejecting state recovers due to maintenance or aging. For this reason, it is necessary to calculate a non-discharge correction coefficient value for adjusting the discharge amount of the nozzle in the vicinity of the discharge nozzle every time non-discharge is detected or every time the non-discharge state is resolved.
However, in order to further reduce the influence of the non-ejection nozzle, it is necessary to calculate the non-ejection correction coefficient value with high accuracy at each image density. . If the calculation takes time, a long time is required from the acquisition of the non-ejection nozzle information to the start of image recording, and there is a problem that the efficiency of image recording cannot be increased.

  SUMMARY OF THE INVENTION An object of the present invention is to solve the problems based on the above prior art, and can cope with the occurrence of a non-ejection nozzle in a short time, and can efficiently record an image and an image recording method. Is to provide.

  In order to solve the above problems, the present invention provides a recording head having a plurality of recording elements that discharge ink droplets, and at least one of the recording head and the recording medium to convey the recording head and the recording medium. A non-uniformity correction coefficient for storing, as one of the recording characteristics of the recording element, a non-uniformity correction coefficient value calculated for each pixel density based on the non-uniformity information for each recording element read in advance with a test pattern. A non-ejection correction coefficient value when a recording element in the vicinity calculated for each pixel density based on the unevenness information for each recording element read in advance with a test pattern for each recording element is non-ejecting. Non-ejection correction coefficient calculation storage means for storing as one of the recording characteristics, non-ejection information detection means for detecting non-ejection information of the recording element, pixel density and each recording element A non-ejection information, a density correction coefficient calculation storage means and a non-ejection correction coefficient calculation storage means for selecting a recording characteristic of the recording element, and a density signal based on the recording characteristics selected by the selection means. An image recording apparatus comprising: a correction processing unit that corrects a pixel density; and a drive control unit that controls driving of the recording element based on an output density corrected by the correction processing unit. .

Here, it is preferable that the non-ejection correction coefficient calculation storage unit calculates and stores a non-ejection correction coefficient value for each position with respect to the non-ejection nozzle.
The non-ejection correction coefficient calculation storage means is an index that associates a lookup table storing a plurality of unevenness correction coefficients, and each printing element and the non-ejection correction coefficient value of the lookup table for each position with respect to the non-ejection nozzle. It is preferable that the index table is associated with the unevenness correction coefficient to a recording element of the unevenness correction coefficient within a certain range of the unevenness correction coefficient stored in the lookup table.
Note that the look-up table (LUT) is a reference table and stores a relationship among nozzles (ejection units), image density, and unevenness correction coefficients. For example, the corresponding unevenness correction coefficient is stored using the nozzle, image density, reference number, and the like as keys.
The correction condition is preferably a condition in which the differential coefficient at the frequency origin of the power spectrum representing the spatial frequency characteristic of density unevenness is substantially zero.
Further, the correction condition is preferably expressed by N simultaneous equations obtained from a condition for storing a direct current component of spatial frequency and a condition that the differential coefficients up to the (N−1) th order are substantially zero.

  In order to solve the above problems, the present invention provides a recording head having a plurality of recording elements that eject ink droplets, and at least one of the recording head and the recording medium to convey the recording head and the recording target. An image recording method for forming an image on the recording medium by the recording head while relatively moving the recording head and the recording medium by the conveying means; A non-uniformity correction coefficient calculation storage step for storing, as one of the recording characteristics of the recording element, a non-uniformity correction coefficient value calculated for each pixel density based on non-uniformity information for each recording element read by the test pattern, and each recording element On the other hand, non-ejection compensation when the neighboring recording elements calculated for each pixel density based on the unevenness information for each recording element read by the test pattern fails. A non-ejection correction coefficient calculation storage step for storing a coefficient value as one of the recording characteristics, a non-ejection information detection step for detecting non-ejection information of the recording element, and a pixel density and non-ejection information of each recording element. A selection step of selecting a recording characteristic of the recording element from the recording characteristics stored in the density correction coefficient calculation storage step and the non-ejection correction coefficient calculation storage step, and a density signal based on the recording characteristics selected by the selection unit. A correction processing step for correcting the pixel density; and an image output step for controlling driving of the recording element based on the output density corrected in the correction processing step and outputting an image on the recording medium. An image recording method is provided.

  According to the present invention, the non-ejection correction information assuming that the recording element is non-ejection is calculated and stored, and the correction information used based on the actual non-ejection information from the stored non-ejection correction information and unevenness correction information By selecting, it is possible to correct unevenness without calculating correction information that takes into account non-ejection each time the non-ejection information changes. As a result, it is possible to record an image in which unevenness is corrected with high accuracy in a short time after detecting non-ejection information.

  An image recording apparatus and an image recording method according to the present invention will be described in detail based on embodiments shown in the accompanying drawings.

FIG. 1 is a front view showing a schematic configuration of an image recording apparatus 10 of an embodiment of the image recording apparatus of the present invention using the image recording method of the present invention, and FIG. 2 is an image recording apparatus 10 shown in FIG. 4 is a top view showing the suction belt conveyance unit 36 and the recording head unit 50 of FIG.
The image recording apparatus 10 basically includes a supply unit 12 that supplies a recording medium P, a conveyance unit 14 that conveys the recording medium P supplied from the supply unit 12 while maintaining flatness, and a conveyance unit 14. A drawing unit 16 disposed opposite to the unit 14 and having a recording head unit 50 for drawing an image on the recording medium P, an ink storage / loading unit 52 for storing ink to be supplied to the recording head unit 50, and the like; A heating / pressurizing unit 18 for heating and pressurizing the recording medium P on which an image is drawn, a discharge unit 20 for discharging the recording medium P on which an image has been drawn to the outside, and a drawing unit 16 on the recording medium P. It has the scanner 24 which reads the recorded image, and the control part 22 which controls these.

The supply unit 12 includes a magazine 30, a heating drum 32, and a cutter 34.
The magazine 30 stores a roll-shaped recording medium P. At the time of image drawing, the recording medium P is supplied from the magazine 30 to the heating drum 32.
The heating drum 32 is disposed on the downstream side of the magazine 30 in the conveyance path of the recording medium P, and the recording medium P sent out from the magazine 30 is bent in a direction opposite to the direction stored in the magazine 30. Heat in state.
By heating the recording medium P by the heating drum 32, the winding habit attached to the recording medium P is removed while being stored in the magazine 30. That is, the heating drum 32 performs a decurling process on the recording medium P.
At this time, it is preferable to control the heating temperature so that the recording medium P is curled outwardly on the printing surface.

The cutter 34 has a fixed blade 34A having a length equal to or longer than the conveyance path width of the recording medium P, and a round blade 34B that moves along the fixed blade 34A, and a surface side on which an image of the recording medium P is drawn. The circular blade 34B is disposed on the surface, and the fixed blade 34A is disposed on the surface facing the conveyance path.
The cutter 34 cuts the recording medium P supplied through the heating drum 32 into a desired size.

  Here, in this embodiment, the supply unit has one magazine. However, the present invention is not limited to this. For example, a plurality of magazines containing recording media having different paper width, paper quality, and type may be arranged. Also, a cassette in which a large number of recording media that have been cut in advance to a predetermined length can be used instead of or in addition to the magazine. When only the recording medium P that has been cut to a predetermined length is used as the recording medium P, the above-described heating roller and cutter are not necessarily provided.

  Further, when a plurality of magazines and / or cassettes are used and a plurality of types of recording paper can be used, an information recording body such as a bar code or a wireless tag in which the paper type information is recorded is used as the magazine and / or cassette. Attach and read the information of the information recording medium with a predetermined reader to automatically determine the type of paper to be used, and perform ink ejection control to realize appropriate ink ejection according to the type of paper Preferably it is done.

  The conveyance unit 14 includes an adsorption belt conveyance unit 36, an adsorption chamber 39, a fan 40, a belt cleaning unit 42, and a heating fan 44. The recording medium P that has been decurled by the supply unit 12 and cut to a predetermined length is provided. The drawing position, that is, the position where the image is drawn by the drawing unit 16 described later is conveyed.

The suction belt conveyance unit 36 is disposed on the downstream side of the cutter 34 in the conveyance path of the recording medium P, and includes a roller 37 a, a roller 37 b, and a belt 38.
The belt 38 is an endless belt having a width that is wider than the width of the recording medium P, and is stretched between rollers 37a and 37b. The belt 38 has a plurality of suction holes (not shown) formed on the belt surface.
Further, it faces at least an image drawing (printing) position of the suction belt conveyance unit 36, that is, a nozzle surface of a recording head unit 50 described later of the drawing unit 16 and an image detection position, that is, a sensor surface of the scanner 24 described later. The portion is held horizontally (flat) with respect to the nozzle surface and the sensor surface.
At least one of the rollers 37a and 37b around which the belt 38 is wound is connected to a motor (not shown), and the power of the motor is transmitted to the belt 38 through at least one of the rollers 37a and 37b. Is driven clockwise in FIG. 1, and the recording medium P held on the belt 38 is conveyed from left to right in FIG.

  Here, the transport means for the recording medium P is not particularly limited, and a roller / nip transport mechanism can be used instead of the suction belt transport section 36. However, when the drawing area is conveyed by a roller / nip, the roller contacts the printing surface immediately after printing, so that there is a problem that the image is likely to spread. Adsorption belt conveyance is preferred.

The suction chamber 39 is provided inside the belt 38 at a position facing a nozzle surface of a recording head unit 50 (described later) of the drawing unit 16 and a sensor surface of the scanner 24. The fan 40 is connected to the suction chamber 39. By sucking the suction chamber 39 with the fan 40 to a negative pressure, the recording medium P on the belt 38 is sucked and held on the belt 38.
By adsorbing the recording medium P to the belt, the recording medium P can be stably held.

The belt cleaning unit 42 is disposed on the outer side of the belt 38, that is, on the side facing the ring-shaped outer peripheral surface, and at a position away from the conveyance path of the recording medium P. That is, the belt 38 passes the drawing unit 16, discharges the recording medium P to a pressure roller 754 described later, and then passes a position facing the belt cleaning unit 42.
The belt cleaning unit 42 removes ink adhering to the belt 38 by performing borderless printing or the like. Examples of the belt cleaning unit 42 include a method of niping a brush / roll, a water absorbing roll, etc., an air blow method of spraying clean air, or a combination thereof. In the case where the cleaning roll is nipped, the cleaning effect is great if the belt linear velocity and the roller linear velocity are changed.

The heating fan 44 is disposed outside the belt 38 and on the upstream side of a recording head unit 50 (to be described later) of the drawing unit 16 on the conveyance path of the recording medium P.
The heating fan 44 blows heated air to the recording medium P before drawing to heat the recording medium P. By heating the recording medium P immediately before drawing, the ink is easily dried after landing.

  The drawing unit 16 includes a recording head unit 50 that draws (prints) an image, and an ink storage / loading unit 52 that supplies ink to the recording head unit 50.

The recording head unit 50 includes recording heads 50K, 50C, 50M, and 50Y, and is disposed to face the surface of the belt 38 on which the recording medium P is placed.
The recording heads 50K, 50C, 50M, and 50Y are piezo-type ink jet heads that discharge black (K), cyan (C), magenta (M), and yellow (Y) ink from the discharge unit, respectively. The recording heads 50 </ b> K, 50 </ b> C, 50 </ b> M, and 50 </ b> Y are arranged in the order closer to the heating fan 44 on the downstream side in the transport direction of the recording medium P from the heating fan 44. Arranged in order. The recording heads 50K, 50C, 50M, and 50Y are connected to the ink storage / loading unit 52 and the control unit 22.
Further, as shown in FIG. 2, the recording heads 50K, 50C, 50M, and 50Y include a plurality of recording heads in a region where the width in the direction orthogonal to the conveyance direction of the recording medium P exceeds the maximum width of the recording medium P to be conveyed. This is a full-line type inkjet head in which ejection portions (nozzles) are arranged in a line. Here, the structure of the inkjet head will be described in detail later together with the relationship with the ink storage / loading unit 52.

  As in this embodiment, the recording head is a full line type, so that the recording medium P and the drawing unit 16 are relatively 1 in the direction (sub-scanning direction) orthogonal to the extending direction of the ejection unit of the recording head. The image can be recorded on the entire surface of the recording medium P by being moved once (that is, by one scanning). Thereby, it is possible to perform high-speed printing as compared with the shuttle type head in which the recording head reciprocates in the main scanning direction, and productivity can be improved.

The ink storage / loading unit 52 includes an ink supply tank that stores ink of a color corresponding to each of the recording heads 50K, 50C, 50M, and 50Y.
As the ink supply tank, for example, a system that replenishes ink into a tank from a replenishing port (not shown) or a cartridge system that replaces the entire tank when the ink remaining amount is low can be used.
Each ink supply tank of the ink storage / loading unit 52 communicates with each recording head 50K, 50C, 50M, 50Y via a pipe line (not shown), and supplies ink to each recording head 50K, 50C, 50M, 50Y. To do.

Here, the ink storage / loading unit 52 includes notifying means (display means, warning sound generating means, etc.) for notifying that when the ink remaining amount is low, and a mechanism for preventing erroneous loading between colors. It is preferable to have.
Further, when the ink type is changed according to the usage, it is preferable to use a cartridge system. Further, it is preferable that the ink type information is identified by a bar code or the like, and discharge control is performed according to the ink type.

  Next, the structure of the recording heads 50K, 50C, 50M, and 50Y will be described. Here, since the recording heads 50K, 50C, 50M, and 50Y have the same configuration except for the color of ink to be ejected, the recording head 50K will be described below as a representative.

3A is a front view showing an arrangement pattern of the ejection units 60 of the recording head 50K, and FIG. 3B is an enlarged cross-sectional view showing one ejection unit 60 of the recording head 50K.
As shown in FIG. 3A, the recording head 50K includes a plurality of recording elements (hereinafter referred to as “ejection units”) 60 that eject ink droplets. The plurality of ejection units 60 are arranged in a row at regular intervals.

  As shown in FIG. 3B, one ejection unit 60 includes an ink chamber unit 61 and an actuator 66. Further, the ink chamber unit 61 is connected to the common flow path 65. The common flow path 65 is connected to the ink chamber units 61 of the plurality of ejection units 60.

The ink chamber unit 61 includes a nozzle 62, a pressure chamber 63, and a supply port 64.
The nozzle 62 is an opening for ejecting ink droplets, and has one end opened on a surface facing the recording medium P and the other end connected to the pressure chamber 63.
The pressure chamber 63 has a rectangular parallelepiped shape whose plane shape perpendicular to the direction in which the ink droplets are ejected, and both corners on the diagonal are connected to the nozzle 62 and the supply port 64.
The supply port 64 has one end connected to the pressure chamber 63 and the other end communicating with the common flow path 65.

The actuator 66 is disposed on a surface (top surface) opposite to the connection surface between the nozzle 62 and the supply port 64 of the pressure chamber 63, and includes a pressure plate 67 and an individual electrode 68.
The actuator 66 deforms the pressure plate 67 by applying a driving voltage to the individual electrode 68.

An ink discharge method of the discharge unit 60 will be described.
Ink is supplied from the common flow path 65 to the pressure chamber 63 and the nozzle 62 via the common port 64.
When a drive voltage is applied to the individual electrode 68 while the pressure chamber 63 and the nozzle 62 are full of ink, the pressure plate 67 is deformed, the pressure chamber 63 is pressurized, and ink is ejected from the nozzle 62. The By driving the actuator 66 in this way, ink droplets can be ejected from the nozzle 62.
When ink is ejected, new ink is supplied from the common flow path 65 through the supply port 64 to the pressure chamber 63.

  In addition, the arrangement structure of the discharge part of this invention is not limited to the example of illustration. In this embodiment, a method of ejecting ink droplets by deformation of an actuator 66 typified by a piezo element (piezoelectric element) is adopted. However, the present invention is not limited to this, and a method of ejecting ink is particularly used. Without being limited thereto, various methods such as a thermal jet method in which bubbles are generated by heating ink with a heating element such as a heater and ink droplets are ejected by the pressure can be applied instead of the piezo method.

Next, the relationship between the recording head unit 50 and the ink storage / loading unit 52 will be described in more detail.
FIG. 4 is a schematic diagram illustrating a configuration of an ink supply system and a head peripheral portion in the image recording apparatus 10. Since the relationship between the recording heads 50K, 50C, 50M, and 50Y and the ink storage / loading unit 52 is the same except for the type of ink, the recording head 50K and the ink storage / loading are hereinafter described. Only the relationship with the unit 52 will be described, and the description of the relationship between the recording heads 50C, 50M, and 50Y and the ink storage / loading unit 52 will be omitted.

The ink supply tank 70 is a tank that stores a color corresponding to the recording head 50 </ b> K, that is, black ink, and is disposed inside the ink storage / loading unit 52. The recording head 50K and the ink supply head 70 are connected by a supply pipe.
A filter 72 is provided in the middle of the flow path connecting the ink supply tank 70 and the recording head 50K to remove foreign substances and bubbles. The filter mesh size of the filter 72 is preferably equal to or smaller than the nozzle diameter (generally about 20 μm).

  A sub tank is preferably provided in the vicinity of the recording head 50K or integrally with the recording head 50K. By providing the sub tank, it is possible to obtain a damper effect that prevents fluctuations in the internal pressure of the head, and to improve refill.

  As shown in FIG. 4, the image recording apparatus 10 includes a cap 74, a suction pump 77, a recovery tank 78, and a recording head as means for preventing the nozzle 62 from drying or preventing an increase in ink viscosity near the nozzle. A cleaning blade 76 is provided as a cleaning means for the 50K nozzle surface, that is, the surface on which the opening of the nozzle 62 is formed.

  The maintenance unit including the cap 74 and the cleaning blade 76 can be moved relative to the recording head 50K by a moving mechanism (not shown), and is moved from a predetermined retracted position to a maintenance position below the recording head 50K as necessary. .

The cap 74 is disposed at a position facing the recording head 50K in the maintenance position, and is supported so as to be movable up and down relatively with respect to the recording head unit 50 by a lifting mechanism (not shown).
The cap 74 is raised to a predetermined raised position by an elevating mechanism (not shown) when the power is turned off or during printing standby, is in close contact with the recording head 50K, and covers the nozzle surface of the recording head 50K with the cap 74.
In this manner, the cap 74 covers the nozzle surface of the recording head 50K and seals it, so that the ink in the nozzles is dried and fixed, and the ink solvent evaporates to increase the ink viscosity. Can be prevented.

Further, the cap 74 may be attached to the recording head 50K at the time of maintenance or at regular intervals, and the actuator 66 may be driven to eject ink from the nozzles 62.
In the recording head 50K, if the frequency of use of a specific nozzle 62 is low during drawing or standby, and ink is not ejected for a certain period of time, the ink solvent near the nozzle evaporates and the ink viscosity increases. As a result, the ink may not be ejected from the nozzle 62, but the ink is preliminarily ejected to the cap 74 (purge, idle ejection, spit) and the deteriorated ink in the nozzle 62 (near the nozzle whose viscosity has increased). Ink) can be discharged from the nozzle 62. Thereby, it is possible to prevent the nozzle 62 from being clogged with ink, and it is also possible to prevent the discharge characteristics from being changed due to different ink viscosities depending on the nozzle 62. Thereby, ink droplets can be stably discharged.

The suction pump 77 has one end connected to the cap 74 and the other end connected to the recovery tank 78. The cap 74 is attached to the recording head 50K, and the ink in the nozzle 62 is sucked out by sucking with the suction pump 77 in a state where the cap 74 and the recording head 50K are in close contact with each other. Further, the ink sucked by the suction pump 77 is sent to the collection tank 78.
Thus, by sucking ink by the suction pump 77, for example, bubbles are mixed into the ink (in the pressure chamber 63) in the recording head 50K, and the ink can be ejected from the nozzle even if the actuator 66 is operated. Even if it cannot, the ink in the pressure chamber 63 (ink mixed with bubbles) can be removed by suction by sucking the ink with the suction pump 77. That is, the ink droplets can be ejected.
The suction by the suction pump 77 is preferably performed in order to suck out the deteriorated ink whose viscosity has been increased (solidified) even when the ink is initially loaded into the head or when the ink is used after being stopped for a long time.
Further, since the suction by the suction pump 77 is performed on the entire ink in the pressure chamber 63, the amount of ink consumption increases. Accordingly, when the increase in the viscosity of the ink is small, it is preferable to discharge the ink droplets (preliminary discharge) onto the cap 74 described above.

The cleaning blade 76 is formed of an elastic member such as rubber, and is arranged in contact with the nozzle surface of the recording head 50K during maintenance. The cleaning blade 76 is connected to a blade movement mechanism (wiper) (not shown), and is slid on the nozzle surface by the blade movement mechanism. As the cleaning blade 76 slides on the nozzle surface, ink droplets and foreign matter adhering to the nozzle surface are wiped off. That is, the nozzle surface can be cleaned.
In addition, it is preferable to perform preliminary ejection in order to prevent foreign matter from being mixed into the nozzle 62 by the blade when the dirt on the ink ejection surface is cleaned by the blade mechanism.

Returning to FIG. 1, another part of the image recording apparatus 10 will be described.
The heating and pressing unit 18 includes a post-drying unit 53 and a pressure roller pair 54, and heats and presses the recording medium P on which an image is drawn by the drawing unit 16, thereby drying the image unit. Let it settle.
The post-drying unit 53 is disposed on the downstream side of the recording head unit 50 in the conveyance path of the recording medium P and at a position facing the belt 38. The post-drying unit 53 is a heating fan or the like, and blows hot air on the image surface of the recording medium P to dry the drawn image.
Here, it is preferable to use a heating fan and blow hot air on the post-drying section 53.
By drying the ink in the image area on the recording medium with the heating fan, the ink can be dried without contacting the image area. As a result, it is possible to prevent image defects and image smearing from occurring on the image drawn on the recording medium P.

The pressure roller pair 54 is disposed on the downstream side of the post-drying unit 53 in the conveyance path of the recording medium P. The pressure roller pair 54 sandwiches and conveys the recording medium P separated from the belt 38 after passing through the post-drying unit 53.
The pressure roller pair 54 is a means for controlling the glossiness of the image surface. The pressure roller pair 54 has a predetermined surface uneven shape while heating the image surface of the recording medium P conveyed by the suction belt conveyance unit 36. Pressure is applied by the pressure roller 54 to transfer the uneven shape to the image surface.

  In addition, when printing on porous paper with dye-based ink, it is possible to prevent contact with things that cause destruction of dye molecules, such as ozone, by blocking the paper holes by pressurization. The weather resistance of can be improved.

Further, in the image recording apparatus 10, a cutter (second cutter) 56 is disposed on the downstream side of the heating and pressing unit 18 in the conveyance path of the recording medium P.
The cutter 56 includes a fixed blade 56A and a round blade 56B. When a normal image and an image for detecting displacement are formed on the recording medium P, a normal image portion and an image portion for detecting displacement are formed. Disconnect.

The discharge unit 20 includes a first discharge unit 58A and a second discharge unit 58B, and is disposed on the downstream side of the cutter 56 in the conveyance direction of the recording medium P. The discharge unit 20 discharges the recording medium P on which the image is fixed by the heating and pressing unit 18.
Here, in the present embodiment, according to the image recorded on the recording medium P, a sorting unit (not shown) switches the discharging unit that discharges the recording medium P, and a normal image is drawn on the first discharging unit 58A. The recording medium thus discharged is discharged, and the recording medium on which the image used for the positional deviation detection is drawn and unnecessary recording medium are discharged to the second discharge section 58B.

  Further, it is preferable that the discharge unit 20 is provided with a sorter for collecting images according to orders.

  As in the present embodiment, it is preferable to provide two discharge units so that the discharge unit can be selected according to the purpose. However, the present invention is not limited to this. The medium may be discharged from one discharge unit. Moreover, you may provide three or more discharge parts.

  Next, the control unit 22 controls conveyance, heating, drawing, image detection, and the like of the recording medium by the supply unit 12, the conveyance unit 14, the drawing unit 16, the heating and pressing unit 18, the discharge unit 20, and the scanner 24. The configuration of the control unit 22 will be described in detail later.

  The scanner 24 faces the outer side (outer peripheral surface) of the belt 38 and is disposed at a position between the recording head unit 50 and the post-drying unit 53. The scanner 24 has an image sensor (line sensor or the like) for imaging (that is, reading) a test pattern formed by the drawing unit 16, and reads an image recorded on a recording medium by the image sensor. The scanner 24 can read an image at at least two different resolutions, and switches the resolution to be read depending on the mode.

  The scanner 24 of the present embodiment is configured by a line sensor having a light receiving element array wider than the ink ejection width (image recording width) by the recording heads 50K, 50C, 50M, and 50Y. The line sensor includes an R sensor array in which photoelectric conversion elements (pixels) provided with a red (R) color filter are arranged in a line, a G sensor array provided with a green (G) color filter, A color separation line CCD sensor including a B sensor array provided with a blue (B) color filter. Instead of the line sensor, an area sensor in which the light receiving elements are two-dimensionally arranged can be used.

FIG. 5 is a principal block diagram showing the system configuration of the control unit 22 of the image recording apparatus 10.
The control unit 22 includes a communication interface 102, a system controller 104, an image memory 106, a motor driver 108, a heater driver 110, a print control unit 112, an image buffer memory 114, a head driver 116, and the like. The conveyance unit 14, the drawing unit 16, the heating and pressurizing unit 18, the discharge unit 20, and the conveyance, heating, drawing, and misregistration detection of the recording medium P by the scanner 24 are controlled.

  The system controller 104 is a control unit that controls each unit such as the communication interface 102, the image memory 106, the motor driver 108, the heater driver 110, and the like. The system controller 104 includes a central processing unit (CPU) and its peripheral circuits, and performs communication control with the host computer 118, read / write control of the image memory 106, and the like, as well as a transport system motor 98 and heater 99. A control signal for controlling is generated.

  Further, the system controller 104 generates a recording characteristic calculation unit 130 that generates recording characteristic data of each ejection unit such as a landing position error and a droplet diameter from the test pattern read data read from the scanner 24, and a recording of each ejection unit. And a correction coefficient calculation unit 132 that calculates a correction coefficient when there is an unevenness correction coefficient and a non-ejection nozzle from the characteristics. The recording characteristic calculation method by the recording characteristic calculation unit 130 and the unevenness correction coefficient and non-ejection correction coefficient calculation method by the correction coefficient calculation unit 132 will be described in detail later. The recording characteristic calculation unit 130 and the correction coefficient calculation unit 132 process information by ASIC, software, or an appropriate combination.

The correction coefficient storage unit 120 is a storage unit that stores unevenness correction coefficient data and non-ejection correction coefficient data calculated by the correction coefficient calculation unit 132, and is necessary among the stored unevenness correction coefficient and non-ejection correction coefficient. Data is sent to the print control unit 112.
Note that the formats of the unevenness correction coefficient data and the non-ejection correction coefficient data are not particularly limited, and may be stored as mathematical expressions or LUTs (look-up tables).

  The ROM 122 stores a program executed by the CPU of the system controller 104, various data necessary for control (including test pattern data for landing position error measurement), and the like. The ROM 122 may be a non-rewritable storage unit, or may be a rewritable storage unit such as an EEPROM. Further, by utilizing the storage area of the ROM 122, the ROM 122 may have the function of the correction coefficient storage unit 120.

  The communication interface 102 receives image data sent from the host computer 118 and sends it to the system controller 104. As the communication interface 102, a serial interface such as USB, IEEE 1394, Ethernet (registered trademark), a wireless network, or a parallel interface such as Centronics can be used. Furthermore, a buffer memory for speeding up communication may be installed.

The image memory 106 is a storage unit that temporarily stores an image input via the communication interface 102, and data is read and written through the system controller 104. The image memory 106 is not limited to a memory composed of semiconductor elements, and a magnetic medium such as a hard disk may be used.
Image data sent from the host computer 118 is taken into the image recording apparatus 10 via the communication interface 102 and stored in the image memory 106 via the system controller 104.

The motor driver 108 is a driver (drive circuit) that drives the motor 98 in accordance with an instruction from the system controller 104.
The heater driver 110 is a driver that drives the heater 99 such as the post-drying unit 746 in accordance with an instruction from the system controller 104.

The print control unit 112 includes a density data generation unit 136, a correction processing unit 138, an ink ejection data generation unit 140, and a drive waveform generation unit 142, and is controlled according to the control of the system controller 104. Various processes for generating a signal for printing control from image data in the image memory 106, density unevenness correction, and the like are performed, and a printing control signal (printing data) generated from the image data is supplied to the head driver 116.
Control of the ejection timing of the ink droplets of the recording head 750 is performed via the head driver 116 based on the image data that has undergone the required signal processing in the print control unit 112. Thereby, a desired dot arrangement is realized.

  The density data generation unit 136 is a signal processing unit that generates initial density data for each ink color from input image data, and performs density conversion processing (including UCR processing and color conversion) and, if necessary, pixel number conversion. Process.

  The correction processing unit 138 is a processing unit that performs density correction calculation using the unevenness correction coefficient and the non-ejection correction coefficient stored in the correction coefficient storage unit 120, and performs density unevenness correction processing.

  The ink ejection data generation unit 140 is a signal processing unit including a halftoning processing unit that converts density data after correction generated by the correction processing unit 138 into binary (or multi-value) dot data. Multi-value processing is performed. The ink discharge data generated by the ink discharge data generation unit 140 is given to the head driver 116, and the ink discharge operation of the head 50 is controlled.

  The drive waveform generator 142 is a means for generating a drive signal waveform for driving the actuator 66 corresponding to each nozzle 61 of the head 50. The signal (drive waveform) generated by the drive waveform generation unit 142 is supplied to the head driver 116. Note that the signal output from the drive signal generation unit 142 may be digital waveform data or an analog voltage signal.

  In addition, the density data generation unit 136, the correction processing unit 138, the ink ejection data generation unit 140, and the drive waveform generation unit 142, which are signal processing units, process information by ASIC, software, or an appropriate combination. Do.

  The image buffer memory 114 temporarily stores data such as image data and parameters in the image buffer memory 114 when image data is processed in the print control unit 112. In FIG. 5, the image buffer memory 114 is shown in a mode associated with the print control unit 112, but it can also be used as the image memory 106. Also possible is an aspect in which the print control unit 112 and the system controller 104 are integrated and configured with a single processor.

Next, the head driver 116 drives the actuators of the discharge units of the recording heads 50K, 50C, 50M, and 50Y of the respective colors based on the discharge control signal (print data) given from the print control unit 112. The head driver 116 may include a feedback control system for keeping the head driving conditions constant.
The image recording apparatus 10 is basically configured as described above.

Here, FIG. 6 is a flowchart showing a procedure at the time of image output.
The illustrated process is executed by the control unit 22 every time an image is output.
When outputting (printing) an image, first, data of an image to be output (image to be printed) is input (step S20). The data format of the image at the time of input is not particularly limited. For example, it is RGB data of 24-bit color. The input image is subjected to density conversion processing using a lookup table (step S22), and converted into density data D (ij) corresponding to the ink color of the printer. Note that (i, j) represents the position of the pixel, and density data is assigned to each pixel. Here, for convenience of explanation, it is assumed that the resolution of the input image and the resolution of the printer (nozzle resolution) are the same. However, if they do not match, the number of pixels of the input image is converted according to the printer resolution. Processing is performed.

The density conversion process in step S22 is a general process, such as an under color removal (UCR) process, or a distribution process to light ink in the case of a system using light ink (same color light ink). Is included.
For example, in the case of a three-color ink configuration of C (cyan), M (magenta), and Y (yellow), it is converted into CMY density data D (i, j). Alternatively, in the case of a system including other inks such as K (black), LC (light cyan), and LM (light magenta) in addition to the above three colors, the density data D (i, j) including the ink color is included in the density data D (i, j). Converted.

  Correction processing using the calculated unevenness correction coefficient and non-ejection correction coefficient is performed on the density data D (i, j) obtained through the density conversion process (step S24). Detailed processing contents of the unevenness correction coefficient and the non-ejection correction coefficient will be described with reference to FIGS. In this way, corrected density data D ′ (i, j) is obtained.

  Next, halftone processing (screening) is performed from the corrected density data D ′ (i, j) (step S26), thereby including dot on / off signals (binary data) or dot size modulation. In this case, the data is converted into multi-value data including dot type (dot size selection). The method of halftoning is not particularly limited, and a known binary (multi-value) method such as an error diffusion method or a dither method can be used.

  Based on the binary (multi-value) signal thus obtained, droplet ejection from each nozzle is executed, and an image is output (step S28). That is, ink ejection (droplet ejection) data of each nozzle is generated from binary (multi-value) data obtained from the halftoning process (step S26), and the ejection operation is controlled. Thereby, density unevenness is suppressed, and high-quality image formation is possible.

Next, a method for creating the unevenness correction coefficient and the non-ejection correction coefficient by the image recording apparatus 10 will be described. That is, a recording characteristic detection method by the recording characteristic calculation unit 130, a nonuniformity correction coefficient calculation method and a non-ejection correction coefficient calculation method by the correction coefficient calculation unit 132 will be described.
Note that the method of creating the unevenness correction coefficient and the non-ejection correction coefficient is performed in the same manner in any of the recording heads 50K, 50C, 50M, and 50Y, and therefore, the recording head 50K will be described below as a representative.

First, in order to detect the recording characteristics of each ejection unit (recording element), a test pattern is drawn on the recording medium P by the recording head 50K.
FIG. 7A is a schematic diagram illustrating an example of a test pattern, and FIG. 7B is a partially enlarged view of FIG. 7A.
Specifically, when a plurality of discharge units arranged in a row as described above are defined as A1, A2, A3,. Based on the number, the discharge unit is divided into four groups 4k-3, 4k-2, 4k-1, 4k (k = 1, 2, 3,...), And the discharge unit number is 4k-3. The ink droplets are continuously ejected from the recording medium P to form a straight line for each ejection portion, and then the ink droplets are continuously ejected from the ejection portion whose ejection portion number is 4k-2, A straight line for each ejection unit is formed on the recording medium P, and thereafter, similarly, the ejection unit with the ejection unit number 4k-1 and the ejection unit with the ejection unit number 4k are also ejected on the recording medium P. Each straight line is formed.
Further, by grouping the ejection portions that are spaced apart by a certain distance, it is possible to form a straight line without ejecting ink from adjacent ejection portions. Thereby, it can prevent that a straight line overlaps.
In this embodiment, while the recording medium P is transported in the transport direction, that is, the direction perpendicular to the recording head 50K by the transport unit 14, ink droplets are ejected from the respective ejection portions of the recording head 50K onto the recording medium. Forms a droplet injection point.
As described above, as shown in FIGS. 7A and 7B, on the recording medium P, four (G1, G2, G3, and G4) corresponding to the four groups of ejection units are formed. G4) formed, and in each group, a test pattern in which a straight line corresponding to each discharge portion is formed is formed.
In this embodiment, a plurality of types of droplet ejection points can be formed by changing the number of droplets that each recording element drops on one droplet ejection point. Therefore, a test pattern is prepared for each type of droplet ejection point. The test pattern may be recorded on a single recording medium, or may be recorded on a plurality of test patterns. However, by recording on a single recording medium, the test pattern will be described later with higher accuracy. Recording characteristics can be measured.

Next, the recording characteristics of each ejection unit are measured from the produced test pattern.
First, a test pattern formed on the recording medium P is read.
Specifically, after the test pattern is formed, the recording medium P is further transported by the transport unit 14 and passes through a position facing the scanner 24.
The scanner 24 reads the test pattern by reading the image formed on the recording medium P that passes through the facing position. The scanner 24 sends the read image data to the recording characteristic calculation unit 130 of the control unit 22 to the first density unevenness correction information calculation unit 124.

Next, the recording characteristic calculation unit 130 calculates the recording characteristic of each ejection unit, in the present embodiment, the landing position based on the test pattern.
Specifically, the recording characteristic calculation unit 130 calculates the landing positions of the ink droplets in each ejection unit from the image data obtained by reading a test pattern in which a straight line is formed for each ejection unit.
Here, for example, as described in Japanese Patent Application Laid-Open No. 2006-264069, the landing position is determined by detecting the concentration profile of each straight line and calculating the center of each straight line from the detection result. It is possible to calculate the landing position of the ink droplet ejected from.
Further, the calculation method of the center position is not particularly limited, and both ends of the ink droplet may be detected, and the middle point may be the center or the position having the highest density may be the center.
Further, it is preferable that the landing position is calculated at a plurality of points on each straight line, and an approximate straight line is calculated by connecting the centers. By calculating an approximate line by connecting the centers of a plurality of points, the landing position of the ink droplet can be detected more accurately.
Further, by extending the approximate straight line, the relative positional relationship between the groups can be accurately detected. The relative positional relationship may be such that a reference ejection part is set when a test pattern is created, and straight lines formed by the ejection parts are formed by all four groups.
Based on the landing position of the landing point calculated in this way, a difference (landing position error) from the ideal landing position of the droplet landing point (a predicted landing position of the droplet landing point) is calculated.

Next, an example of calculating the unevenness correction coefficient and the non-ejection correction coefficient will be described.
Here, FIGS. 8 and 9 are flowcharts showing calculation examples of the unevenness correction coefficient and the non-ejection correction coefficient. Here, an example will be described in which a correction coefficient at each density is calculated in order to obtain a correction coefficient (unevenness correction coefficient and non-ejection correction coefficient) according to the pixel density.

First, in the following flowchart, the process of calculating the unevenness correction coefficient and the non-ejection correction coefficient (step S102) is repeated for all widths, that is, all nozzles (nzl = 0 to N).
First, it is assumed that the selected nozzle (nozzle number nzl) is non-ejection, and only non-ejection information corresponding to the nozzle is turned ON (step S104). That is, the assumed non-ejection information that the selected nozzle is non-ejection is created.

  Here, the following flowchart is a process (step for calculating a correction coefficient for each density with a predetermined step size (for example, a step of “0.5”) in a pixel density range of “0.0 to 1.0”. S110) is repeated.

For the calculation target density (d), first, the dot drop rate is calculated (step S121).
That is, the dot droplet ejection rate (dp_buf [kind]) corresponding to the target pixel density (d) is calculated using a dot droplet ejection rate table indicating the abundance ratio of the dot type at each image density. The dot stagnation rate table (DP_buf [d] [kind]) is a table having density [d] and dot type [kind] as variables.
FIG. 10 shows an example of a dot ejection rate table (DP_buf [d] [kind]). FIG. 10 illustrates a case where there are four types of dots (kind = [l, 2.3, 4]). In the figure, the horizontal axis represents the pixel density, and the vertical axis represents the droplet ejection type (dot type) ratio. For example, when looking at the ratio of each dot type when the pixel density is 0.8, the ratio of “3 drops” is the highest, about 0.72, then the ratio of “4 drops” is about 0.24, and “2 drops”. The ratio is about 0.04, and the ratio of “1 drop” is 0.0. Thus, the ratio of each dot type at a certain pixel density value is set as the value of dp_buf.

A dot ejection rate table having a relationship as shown in FIG. 11 is created and stored in advance. Note that the dot ejection rate table may be used after being interpolated as necessary.
After determining the dot droplet ejection rate for the calculation target density as described above, next, an effective droplet ejection error is calculated (step S122 in FIG. 8). That is, in step S122, for each nozzle, a calculation is performed to convert the position error data measurement value (err_x [nzl] [kind]) for each dot type into an effective droplet ejection error (position: err_xx [nzl]).
The component of “position: err_xx [nzl]” in the effective droplet ejection error is calculated by the following equation.

すなわち、実行打満誤差の「位置：ｅｒｒ＿ｘｘ［ｎｚｌ］」は、着弾位置誤差の測定値をドット打滴率（ｄｐ＿ｂｕｆ［ｋｉｎｄ］）と打滴液量（ｖｏｌｕｍｅ［ｋｉｎｄ］）で重み付けして加重平均をとったものである。なお、打滴液量（ｖｏｌｕｍｅ［ｋｉｎｄ］）のテーブルは、予めドット種毎の液量を測定して記憶しておくものとする。図１１に打滴液量のテーブルの一例を示す。

In other words, “position: err_xx [nzl]” of the execution stroke error is weighted by weighting the measured value of the landing position error with the dot ejection rate (dp_buf [kind]) and the droplet ejection volume (volume [kind]). It is an average. The droplet ejection volume (volume [kind]) table is measured and stored in advance for each dot type. FIG. 11 shows an example of a droplet ejection volume table.

After step S122 in FIG. 8, the process proceeds to step S123, where the density correction coefficient (coef [nzl]) is calculated and corrected. In order to make the explanation easy to understand, a simple specific example will be described. For example, a case will be described in which the unevenness correction coefficient and the non-ejection correction coefficient are calculated using the correction target nozzle and three nozzles each of the right and left nozzles as a correction window (N = 3). In this case, the correction coefficient for the left nozzle in the correction window is stored in p [0], the correction coefficient for the center nozzle is stored in p [1], and the correction coefficient for the right nozzle is stored in p [2].
Further, in the calculation, cases are classified based on the number and positions of the non-ejection nozzles in the correction window based on the non-ejection information (npn [nzl]) of the head (see FIG. 8). In this example, when there are two or more non-ejection nozzles in the correction window, the calculation is stopped. A specific calculation example is shown in FIG.

The calculation described below is repeated for all nozzles of the head (step S130).
First, a correction window to be calculated is determined and divided into the following three patterns according to the number and position of non-ejection nozzles in the correction window. That is, (a) when there is no non-ejecting nozzle, (b) when the central nozzle is non-ejecting, (C) when the left or right nozzle is non-ejecting, the pattern is divided into three patterns and switched to the corresponding process. .

そして、当該位置誤差情報（ａ［３］）を用いて補正係数（ｐ［３］）を演算する。この演算は、後ほど詳述する。ここでは、表記の便宜上、補正ウインドウ内のノズル位置を表す［０］、［１］、［２］の３種類をまとめて［３］と表記している。
なお、位置誤差情報（ａ［３］）の示す位置誤差が所定のしきい値（例えば、０．１μｍ）内であれば、実質的に補正不要であるとして位置補正を行わないものとする。補正を行うか否かの判断基準となるしきい値は、誤差を許容できる許容範囲の観点から定められる。
当該補正ウインドウ内の各ノズルの補正係数は、次式によって算出される。

さらに、中央ノズル（ｐ［１］）に対しては、１を減ずる。すなわち、次式のように演算する。

(A) When there is no non-ejection nozzle, the following processing is performed.
The ideal position interval value: L is added to the position error of each nozzle (left: -L, center: 0, right: + L), and converted to an absolute position (a [3]). That is, the following calculation is performed.

Then, the correction coefficient (p [3]) is calculated using the position error information (a [3]). This calculation will be described in detail later. Here, for convenience of description, three types of [0], [1], and [2] representing nozzle positions in the correction window are collectively expressed as [3].
If the position error indicated by the position error information (a [3]) is within a predetermined threshold value (for example, 0.1 μm), the position correction is not performed because it is substantially unnecessary. A threshold value that is a criterion for determining whether or not to perform correction is determined from the viewpoint of an allowable range in which an error can be allowed.
The correction coefficient for each nozzle in the correction window is calculated by the following equation.

Further, 1 is subtracted from the central nozzle (p [1]). That is, the calculation is performed as in the following equation.

Next, the correction coefficient in the correction window obtained above is added to the unevenness correction coefficient (coef [nzl]). That is, the calculation is performed as follows.

(B) When the central nozzle does not eject, the following process is performed.
The ideal position interval value: L is added to the position error of each nozzle (left: -L, center: 0, left: + L), and converted to an absolute position (a [3]) (see [Equation 2]) . Then, a correction coefficient (p [3]) is calculated using the position error information (a) [3]. This calculation is performed excluding non-ejection nozzles. In other words, the undischarged central nozzle is calculated as “not present”.
The correction coefficient for each nozzle in the correction window is calculated by the following equation.

Further, −1 is substituted for the central nozzle (p [1]).

Then, the correction coefficient in the correction window obtained above is added to the unevenness correction coefficient (coef [nzl]).
That is, the calculation is performed as follows.

さらに、中央ノズル（ｐ［１］）に対しては、１を減ずる。

また、左ノズル（ｐ［０］）には、０を代入する。

また、右ノズルが不吐出のとき、当該補正ウインドウ内の各ノズルの補正係数は、次式によって算出される。

右ノズルが不吐の時：
さらに、中央ノズル（ｐ［１］）に対しては、１を減ずる。

また、右ノズル（ｐ［２］）には、０を代入する。

(C) When the left or right nozzle does not discharge, the following processing is performed.
The ideal position interval value: L is added to the position error of each nozzle (left: -L, center: 0, right: + L) and converted to an absolute position (a [3]) (see [Equation 2]) . Then, the correction coefficient (p [3]) is calculated using the position error information (a [3]). This calculation is performed excluding non-ejection nozzles. That is, the non-discharge left nozzle or the right nozzle is calculated as “nothing”.
When the left nozzle does not eject, the correction coefficient for each nozzle in the correction window is calculated by the following equation.

Further, 1 is subtracted from the central nozzle (p [1]).

Also, 0 is substituted for the left nozzle (p [0]).

When the right nozzle is not ejecting, the correction coefficient of each nozzle in the correction window is calculated by the following equation.

When the right nozzle fails:
Further, 1 is subtracted from the central nozzle (p [1]).

Also, 0 is assigned to the right nozzle (p [2]).

Then, the correction coefficient in the correction window obtained above is added to the unevenness correction coefficient (coef [nzl]).
That is, the calculation is performed as follows.

The above calculation is repeated for all nozzles in the head (step S130).
For each pixel density, the same processing is sequentially performed, and then the correction coefficient (coef [j]) at each pixel density is determined as the unevenness correction coefficient (COEF [d] [j]) and the non-ejection left neighbor correction coefficient (L_COEF). [D] [j]), the non-ejection right neighbor correction coefficient (R_COEF [d] [j]) is moved (step S140). At this time, 1 is added to all data.
Here, as shown in the following equation, the correction coefficient of the nozzle (j = nzl) assumed to be non-ejection is not moved, and the correction coefficient of the nozzle (j = nzl + 1) adjacent to the left of the nozzle assumed to be non-ejection is , L_COEF [d] [j], and the correction coefficient of the nozzle (j = nzl−1) on the right side of the nozzle assumed to be non-ejection is moved to R_COEF [d] [j]. Further, the correction coefficients of the nozzles (j ≠ nzl, nzl-1, nzl + 1) which are not any of the above three are moved to COEF [d] [j].

The above process is executed and the present calculation process is terminated.
As described above, the recording characteristic calculation unit 130 and the correction coefficient calculation unit 132 perform non-ejection when it is assumed that the unevenness correction coefficient and each nozzle (ejection unit) are non-ejection for each image density and for each ejection unit. A correction coefficient is calculated. The calculated unevenness correction coefficient and non-ejection correction coefficient are stored in the correction coefficient storage unit 120.

Next, the flow of image data processing will be described.
FIG. 12 is a flowchart showing the flow of image data processing. As described with reference to FIG. 6, first, image data is read (step S30), and the image density value is converted using the density conversion table for the image table (step S32). Unevenness correction processing is executed on the density data (step S34), and N-value conversion processing (an example based on error diffusion will be described later in this example) is executed on the corrected density data (step S36). Then, droplet ejection is performed based on the obtained N value data (dot data) (step S38).

Next, FIG. 13 shows a detailed example of the unevenness correction process (step S34) shown in FIG.
FIG. 13 is a flowchart for performing unevenness correction.
When this process starts, first, the density unevenness correction coefficient table (COEF [Dmax] [Nnzl]), the non-ejection left adjacent correction coefficient table (L_COEF [Dmax] [Nnzl]), and the non-ejection right adjacent correction coefficient table (R_COEF). [Dmax] [Nnzl]) is read (step S210).
Next, the actually measured non-discharge information (NPN [Nnzl]) is read (step S212). Here, as described above, the measurement non-ejection information is recorded as a test pattern in which a straight line is formed for each nozzle, detects whether or not a straight line corresponding to each nozzle is formed, and detects a non-ejection nozzle. Can be created. The measurement non-ejection information is information that the non-ejection nozzle is turned on and the normal nozzle (nozzle that ejects ink droplets) is turned off.
Next, unevenness / non-ejection selection information (F_npn []) for selecting a table corresponding to each nozzle is created based on the read measurement non-ejection information (step S214).
Specifically, when the left and right nozzles of the target nozzle (nzl) are normal nozzles (NPN [nzl + 1] = OFF and NPN [nzl-1] = OFF), F_npn [nzl] = 0 is set, and the target nozzle When (nzl) is a non-ejection nozzle, F_npn [nzl] = 1, and when the right nozzle of the target nozzle (nzl) is non-ejection (NPN [nzl + 1] = ON), F_npn [nzl] = 2 When the right nozzle of the target nozzle (nzl) is not ejecting (NPN [nzl-1] = ON), F_npn [nzl] = 3.

Then, the process of step S230 below is repeated for the entire range while sequentially changing the position (y value) to be calculated in the height direction (y direction) of the image (step S220).
That is, in step S230, a position to be calculated (value of x) is determined for the image width direction (x direction) in the y value related to the calculation target, and a nozzle number (nzl number) corresponding to the x position is determined for this x position. The unevenness correction coefficient and the non-ejection correction coefficient corresponding to the pixel density d [x] [y] and the nzl value are obtained from the density-specific unevenness correction coefficient table, the non-ejection left adjacent correction coefficient table, and the non-ejection right adjacent correction coefficient table. (Step S232).
When F_npn [nzl] = 0, the corresponding unevenness correction coefficients of nzl and image density d are read from the unevenness correction coefficient table for each density (COEF [d] [nzl]), and the read unevenness correction coefficient is used as the correction coefficient (f ).
When F_npn [nzl] = 1, the correction coefficient (f) is set to a predetermined constant (for example, 0).
When F_npn [nzl] = 2, the corresponding non-ejection correction coefficients of nzl and image density d are read from the non-ejection left side correction coefficient table (L_COEF [Dmax] [Nnzl]), and the read non-ejection correction coefficient (unevenness) is read. Correction coefficient) is a correction coefficient (f).
When F_npn [nzl] = 3, the corresponding non-ejection correction coefficients of nzl and image density d are read from the non-ejection right adjacent correction coefficient table (R_COEF [Dmax] [Nnzl]), and the read non-ejection correction coefficient (unevenness) is read. Correction coefficient) is a correction coefficient (f).
Then, using this correction coefficient (f), a correction calculation is executed according to the following equation (step S234).

Regarding the image width (x direction), steps S232 to S234 are repeated for the entire range of the image width while sequentially changing the position of x (step S230).
When the above correction calculation is completed for all image positions [x] [y], this process ends.

Next, an example of the error diffusion method will be described.
FIG. 14 is a flowchart of the error diffusion method performed in the N-value conversion process (step S36) described in FIG.
When this process starts, first, the error integration buffer is initialized to 0 (step S310). FIG. 15 shows a conceptual diagram of the error integration buffer.

As shown in FIG. 15, the error integration buffer has data storage cells corresponding to positions corresponding to the entire width of the image in the x direction, and can store data for two lines in the y direction. In step S310 in FIG. 14, the data of each cell is initialized to 0 as shown in FIG.
Thereafter, the following processing is repeated for the entire range while sequentially changing the calculation target position (billion of y) in the height direction (y direction) of the image (step S320 in FIG. 14).

  That is, N-value processing is performed in raster order for each x position belonging to the y-value line related to the calculation target. In the N-value conversion procedure, first, an integration error value is added to the density of image data for the target position x in the image width direction. FIG. 16 is an explanatory diagram thereof. Now, for the position of interest x, the accumulated error value at the same position in the error accumulation buffer is added to the image data density, and the density obtained by adding the accumulated error value is (modinp).

Next, a threshold value corresponding to the density value (modinp) is read from a threshold value table for N-folding.
FIG. 17 shows an example of the threshold value table. The illustrated threshold value table is an example in the case of using four types of droplet ejection (binarization), and threshold values of “1 drop” to “4 drops” are defined as T1 to T4 as dot types. .

  Appropriate noise is added to the threshold value read from this threshold value table, and then the droplet ejection type is determined from the density value of the target point. In the case of this example, the droplet ejection type is determined as follows based on the value of “density value + error integrated value” and the magnitude relationship between T1, T2, T3, and T4 (see FIG. 14).

(I) When the value of “density value + error integrated value” is equal to or greater than T4 When the value of “density value + error integrated value” is equal to or greater than T4, an output image at the pixel position [x] [y] (Drip point concentration) is determined to be a dot value of 4 drops (for example, “144” in 8 bits).
The error value of the target point generated by the N-value conversion is a value obtained by subtracting the droplet drop point density from “density value + error integrated value”.

(Ii) When the value of “density value + error integrated value” is T3 or more and less than T4 When the value of “density value + error integrated value” is T3 or more and less than T4, the pixel position [x] The output image (droplet spot density) of [y] is determined as a dot value of 3 drops (for example, “112”).
The error value of the target point generated by this N-value conversion is a value obtained by subtracting the 3 drop droplet ejection point density from “density value + error integrated value”.

(Iii) When the value of “density value + error integrated value” is T2 or more and less than T3 When the value of “density value + error integrated value” is T2 or more and less than T3, the pixel position [x] The output image (droplet spot density) of [y] is determined to be a 2 drop dot value (for example, “80”).
The error value of the target point generated by this N-folding is a value obtained by subtracting the 2 drop injection point concentration from “density value + error integrated value”.

(Iv) When the value of “density value + error integrated value” is T1 or more and less than T2 When the value of “density billion + error integrated value” is T1 or more and less than T2, the pixel position [x] The output image (droplet dot density) of [y] is determined as a dot value of 1 drop (for example, “48”). The error value of the target point generated by this N-folding is a value obtained by subtracting the drop drop point density from “density value + error integrated value”.

(V) When the value of “density value + error integrated value” is less than T1 When the value of “density value + error integrated value” is less than T1, droplet ejection is performed for the pixel position [x] [y]. None (droplet concentration 0). The error value of the target point generated by the N-value conversion is “density value + error integrated value” itself.

Next, a process of diffusing the error value of the target point generated by the N-value conversion of (i) to (v) described above to unprocessed pixels adjacent to the target point is performed.
FIG. 18 is a schematic diagram illustrating an example of an error value diffusion method.
In FIG. 18, the error value generated at the target point [x] is distributed to the four adjacent unprocessed positions at the ratio (distribution constant) shown in FIG.
When the above N-value conversion is completed for all x positions belonging to the target line, the target line (y) is changed. At this time, the error accumulation buffer is updated in preparation for moving the target line (y). That is, as shown in FIG. 19, the error accumulation buffer is scrolled up in the y direction, and the accumulation buffer for a new line is initialized to zero.
In this way, the above process is repeated for all lines corresponding to the image height (y direction), and the process ends when the droplet ejection type is determined for all pixels.
In the N-value conversion processing, the image is converted to N-value using the error dispersion method as described above.

Next, a recording operation by the image recording apparatus 10 will be described.
First, the recording medium P supplied from the magazine 30 of the supply unit 12 is decurled by the heating drum 32 and flattened. Thereafter, the sheet is cut into a predetermined length by the cutter 34 and then supplied to the transport unit 14.
The recording medium P supplied to the conveyance unit 14 is placed on the belt 38 of the suction belt conveyance unit 36 and conveyed along with the rotation of the belt 38.
The recording medium P conveyed by the suction belt conveyance unit 36 passes through a position facing the heating fan 44, is heated to a predetermined temperature, and then passes a position facing the recording head unit 50. When the recording medium P passes through a position facing the recording head unit 50, ink droplets are ejected from each recording head based on the above-described ejection control signal, and K, C, M, and Y are printed on the recording medium. The ink droplets ejected in order land and an image is formed on the recording medium P.
When the recording medium P passes through a position facing the recording head unit 50, the recording medium P is sucked by the suction chamber 39, and the distance between the recording medium P and the recording head unit 50 is constant. Further, a color image is formed on the recording medium P by ejecting the color inks from the recording heads 50K, 50C, 50M, and 50Y while transporting the recording medium P.
The recording medium P on which an image is formed by the recording head unit 50 is further conveyed by the belt 38, passes through a position facing the post-drying unit 53, and the image unit formed of ink is dried and pressurized. After being fixed by the roller 54, it is discharged from the first discharge portion 58A.
As described above, the image recording apparatus 10 draws (records) an image on the recording medium P to produce a print or printed matter.

Hereinafter, the present invention will be described in more detail with reference to FIG.
FIG. 20 is an explanatory diagram conceptually illustrating an example of the relationship among the unevenness correction coefficient and the non-ejection correction coefficient, the image density, the nozzle position (number), and the nonuniformity / non-ejection selection information in the control unit 22. . Here, in the example illustrated in FIG. 20, a description will be given of a case where unevenness caused by a non-ejection nozzle is corrected by two nozzles on the left and right sides of the non-ejection nozzle.

  As shown in FIG. 20, the control unit 22 stores a non-uniformity correction LUT 210 in which non-ejecting nozzles are not included in the left and right nozzles, and a position (−2 position, -1 position, +1 position, +2 position), and non-ejection correction LUTs 212, 214, 216, and 218 in which non-ejection correction coefficients are stored, respectively, and selection means 220. Note that the selection unit 220 is built in the correction processing unit 138.

Here, the unevenness correction LUT 210 stores unevenness correction coefficients for nozzles in which there are no non-ejection nozzles in the two left and right nozzles.
The non-ejection correction LUT (−2 position) 212 stores a non-ejection correction coefficient calculated when it is assumed that the nozzle on the two left side of the nozzle (x) (that is, x−2) is non-ejection. The non-ejection correction LUT 214 stores a non-ejection correction coefficient calculated when it is assumed that the nozzle (x-1) adjacent to the left side of the nozzle (x) is non-ejection, and the non-ejection correction LUT 216 is The non-ejection correction coefficient calculated when the nozzle (x + 1) adjacent to the right side of the nozzle (x) is assumed to be non-ejection is stored, and the non-ejection correction LUT 218 is two right sides of the nozzle (x). The non-ejection correction coefficient calculated when it is assumed that no nozzle (that is, x + 2) is non-ejection is stored.
The unevenness correction LUT 210 and the non-ejection correction LUTs 212, 214, 216, and 218 store correction coefficients for each pixel density and nozzle number.

The selection unit 220 includes a flag table 222 in which uneven / non-ejection selection information for each nozzle is stored, and an LUT switching unit 224, and selects an LUT from which correction coefficients are read based on the flag data and the nozzle (x) number.
The flag table 222 stores unevenness / non-ejection selection information (flag data) for each nozzle number. Here, in this embodiment, there are no non-ejection nozzles in each of the two left and right nozzles, and 0 is used when the correction coefficient of the unevenness correction LUT is used, but the nozzle is a non-ejection nozzle and a constant may be used. When the correction coefficient of the non-ejection correction LUT (−2 position) 212 is used when the left and right nozzles are non-ejection nozzles, the nozzle adjacent to the left side is a non-ejection nozzle and non-ejection correction. 3 is used when the correction coefficient of the LUT (−1 position) 214 is used, and 4 is used when the nozzle adjacent to the right side is a non-ejection nozzle and the correction coefficient of the non-ejection correction LUT (+1 position) 216 is used. However, when the two right nozzles are non-ejection nozzles and the correction coefficient of the non-ejection correction LUT (+2 position) 218 is used, 5 is input. The flag table 222 is created from the result of actually detecting the non-ejection nozzles.
The LUT switching unit 224 reads the flag data (0 to 5) of the corresponding nozzle (x) number from the flag table 222 based on the nozzle (x) number, and the density supplied from the LUT corresponding to the read flag data. The correction coefficient or constant is read and supplied to the correction processing means as a density correction coefficient. At this time, information on the nozzle (x) number and the pixel density of the input image is supplied to each LUT, and each LUT supplies a correction coefficient stored in the corresponding cell.

The control unit 22 is configured as described above, and the nozzle (x) number used for printing is supplied to each LUT and selection means 220, and the pixel density of the input image is supplied to each LUT.
Each LUT extracts a correction coefficient corresponding to the nozzle (x) number and the pixel density. Next, the selection unit 220 reads the corresponding flag data from the flag table 222 based on the nozzle (x) number, and selects the LUT (or constant) to be used. The image data is corrected by using the correction coefficient or constant selected by the selection unit 220 to obtain an output image.

As described above, according to the present invention, the non-ejection correction coefficient when each nozzle becomes non-ejection is calculated and stored together with the unevenness correction coefficient, and the measurement non-ejection actually measured for the non-ejection nozzle. Based on the information, the density unevenness caused by the non-ejection nozzle can be corrected only by switching the non-ejection / non-ejection selection information.
This eliminates the need to newly calculate a correction coefficient that takes into account non-ejection nozzles after detection of the occurrence of non-ejection nozzles, and corrects density unevenness due to non-ejection nozzles in a short time after detection of non-ejection nozzles. Recorded images can be recorded.

Here, in the above embodiment, the LUT in which the correction coefficient is stored for each relationship between each nozzle and the density is created for each positional relationship with the non-ejection nozzle. However, for each positional relationship between the nozzle and the non-ejection nozzle. An index table storing the relationship with the correction coefficient may be provided, and the correction coefficient within the same or a fixed range may be one data. That is, the same correction coefficient on the LUT may be used as the correction coefficient within the same or within a certain range.
In this way, the LUT data to be stored can be reduced by referring to the same data for a plurality of conditions (positional relationship between the nozzle position and the non-ejection nozzle) with the same correction coefficient or within a certain range. can do.

FIG. 21 is an explanatory diagram conceptually illustrating another example of the relationship among the unevenness correction coefficient and the non-ejection correction coefficient in the control unit, the image density, the nozzle position (number), and the nonuniformity / non-ejection selection information.
The control unit 22 ′ illustrated in FIG. 21 includes a non-uniformity correction LUT 210 that stores a non-ejecting nozzle for each of the two left and right nozzles, and a single non-ejecting correction coefficient stored therein. A non-ejection correction LUT 254 and an index table 256 that indicates (determines) the corresponding non-ejection correction coefficient (column) from the non-ejection correction LUT 254 based on the nozzle number.

Here, the unevenness correction LUT 210 stores the unevenness correction coefficient for nozzles in which there are no non-ejection nozzles in the two left and right nozzles, as in the control unit 22.
The non-ejection correction LUT 254 is an LUT in which a plurality of relationships between the pixel density and the correction coefficient are recorded. The non-ejection correction LUT 254 is assigned an index number for each relationship (column) between the pixel density and the correction coefficient.
For each nozzle (x), the index table 256 indicates that the nozzle (x-1) adjacent to the left side of the nozzle (x) is not ejected when the two nozzles on the left side of the nozzle (x) (that is, x-2) are not ejected. For non-ejection, when the nozzle (x + 1) adjacent to the right side of the nozzle (x) is non-ejection, or when the two right nozzles (ie, x + 2) of the nozzle (x) are non-ejection It is stored which data of the LUT 254 is used. That is, the index table 256 stores the index number of the relationship between the pixel density and the correction coefficient that is adapted for each positional relationship between the nozzle (x) and the non-ejection nozzle.
Moreover, since the selection means 220 is the same as the selection means 220 of the control part 20 mentioned above, the description is abbreviate | omitted.

The control unit 22 ′ supplies the nozzle (x) number used for recording to the unevenness correction LUT 210, the index table 256 and the selection unit 220, and supplies the pixel density of the input image to the unevenness correction LUT 210 and the non-ejection correction LUT 254. Is done.
The unevenness correction LUT 210 extracts a correction coefficient corresponding to the nozzle (x) number and the pixel density. Next, the index table 256 determines a non-ejection correction coefficient column to be used for each positional relationship with the non-ejection nozzle from the non-ejection correction LUT 254 based on the nozzle (x) number. Further, the non-ejection correction LUT 254 determines a non-ejection correction coefficient to be used based on the supplied pixel density from the column of non-ejection correction coefficients to be used.
Next, the selection unit 220 reads the corresponding flag data from the flag table 222 based on the nozzle (x) number, and selects the LUT (or constant) to be used. The image data is corrected by using the correction coefficient or constant selected by the selection unit 220 to obtain an output image.
As described above, the data amount can be reduced by providing an index table and using the same or similar tendency correction coefficients as one data.
As in the above-described embodiment, the data can be reduced by using one non-ejection correction LUT. However, for example, when an LUT is provided for each position with respect to the non-ejection nozzle, an index table is provided, The amount of data can be reduced by making the correction coefficient of the same or similar tendency into one data in the LUT.

  Next, a method of creating a non-ejection correction LUT when an index table is provided will be described with reference to FIG. FIG. 22 is a flowchart illustrating a method for creating a non-ejection correction LUT. In the following example, a description will be given of an example in which a non-ejection nozzle is corrected using one left and one right nozzle. In FIG. 22, the correction coefficient for each density (data that summarizes the correction coefficients for each density of one nozzle (hereinafter also referred to as “correction coefficient array”)) is created in the steps shown in FIGS. 8 and 9 described above. The Since the method for creating the correction coefficient sequence is the same as the steps shown in FIGS. 8 and 9, the description thereof is omitted.

After the same processing is sequentially executed for each pixel density by the above-described method, the correction coefficient (coef [j]) at each pixel density is set as the unevenness correction coefficient (COEF [d] [j]), non-ejection left Move to the adjacent correction coefficient (L_COEF [d] [j]) and the non-ejection right adjacent correction coefficient (R_COEF [d] [j]).
As described above, the unevenness correction coefficient (COEF [d] [j]) for each moved nozzle is generated as it is as the unevenness correction LUT. Further, the non-ejection left-side correction coefficient (L_COEF [d] [j]) and non-ejection right-side correction coefficient (R_COEF [d] [j]) for each moved nozzle are determined by the following processing. Furthermore, it is moved.
The calculation described below is repeated for all nozzles of the head (step S150).
First, t = 0 is set (step S152). Here, t is a table number (index number).
Next, it is determined whether or not Lim> (T_COEF [i] [t] −R_COEF [i] [nzl]) ² holds in 0 ≦ i ≦ Dmax (step S154). Here, i is an image density, Lim is an allowable error, and T_COEF [i] [t] is a non-ejection correction coefficient sequence that is already stored in the non-ejection correction LUT. It is a non-ejection correction coefficient sequence having a number t.
In this way, it is determined whether or not an error in each density between R_COEF [i] [nzl] and T_COEF [i] [t] is within a certain range.
If the error in each density is within a certain range, it is registered in the right non-ejection correction coefficient reference table (R_TABLE [nzl], corresponding part of the index table) (step S156). That is, R_TABLE [nzl] = t. That is, when the nozzle number is nzl and the right adjacent nozzle is a non-ejection nozzle, T_COEF [i] [t] is set to be used as the non-ejection correction coefficient.
Thereafter, the process proceeds to step S170.

In step S154, if the error in each density is not within a certain range, t = t + 1 is set (step S158). That is, t is increased by one.
Next, it is determined whether all registered coefficients have been compared (that is, whether t> Tmax) (step S160).
If t ≦ Tmax, the process proceeds to step S154, and it is determined whether Lim> (T_COEF [i] [t] −R_COEF [i] [nzl]) ² holds at the new t.
If t> Tmax, it is determined that it is not within any allowable range of T_COEF [i] [t] already stored, and the process proceeds to step S162.
In step S162, the coefficient is registered in the non-ejection correction coefficient table. Specifically, T_COEF [i] [Tmax + 1] = R_COEF [i] [nzl] in 0 ≦ i ≦ Dmax. That is, R_COEF [i] [nzl] is registered as a non-ejection correction coefficient sequence of T_COEF [i] [Tmax + 1] (that is, Tmax + 1).
Next, the total number of registration coefficients is increased (S164). That is, Tmax is increased by one by setting Tmax = Tmax + 1.
Next, it is registered in the right non-ejection correction coefficient reference table (R_TABLE [nzl], corresponding portion of the index table) (step S166). That is, R_TABLE [nzl] = Tmax. That is, when the nozzle number is nzl and the right adjacent nozzle is a non-ejection nozzle, T_COEF [i] [Tmax] is set to be used as the non-ejection correction coefficient.
Thereafter, the process proceeds to step S170.

In step S170, t = 0.
Next, it is determined whether or not Lim> (T_COEF [i] [t] −L_COEF [i] [nzl]) ² holds in 0 ≦ i ≦ Dmax (step S172).
That is, similarly to the right adjacent non-ejection correction coefficient described above, it is determined whether or not an error in each density between L_COEF [i] [nzl] and T_COEF [i] [t] is within a certain range.
If the error in each density is within a certain range, it is registered in the left non-ejection correction coefficient reference table (L_TABLE [nzl], corresponding part of the index table) (step S174). That is, L_TABLE [nzl] = t. That is, when the nozzle number is nzl and the non-ejection nozzle is on the left, T_COEF [i] [t] is set to be used as the non-ejection correction coefficient.
Thereafter, the number of nozzles (nzl) is increased by 1, and the above process is repeated or the process is terminated.

In step S172, if the error in each density is not within a certain range, t = t + 1 is set (step S176). That is, t is increased by one.
Next, it is determined whether all registered coefficients have been compared (that is, whether t> Tmax) (step S178).
When t ≦ Tmax, the process proceeds to step S172, and it is determined whether Lim> (T_COEF [i] [t] −L_COEF [i] [nzl]) ² holds at the new t.
If t> Tmax, it is determined that it is not within any allowable range of T_COEF [i] [t] already stored, and the process proceeds to step S180.
In step S180, the coefficient is registered in the non-ejection correction coefficient table. Specifically, T_COEF [i] [Tmax + 1] = L_COEF [i] [nzl] when 0 ≦ i ≦ Dmax. That is, L_COEF [i] [nzl] is registered as a non-ejection correction coefficient sequence of T_COEF [i] [Tmax + 1] (that is, Tmax + 1).
Next, the total number of registration coefficients is increased (S182). That is, Tmax is increased by one by setting Tmax = Tmax + 1.
Next, it is registered in the left non-ejection correction coefficient reference table (L_TABLE [nzl], corresponding part of the index table) (step S184). That is, L_TABLE [nzl] = Tmax. That is, when the nozzle number is nzl and the non-ejection nozzle is on the left, T_COEF [i] [Tmax] is set to be used as the non-ejection correction coefficient.
Thereafter, the number of nozzles (nzl) is increased by 1, and the above process is repeated or the process is terminated.
By repeating the above processing, the non-ejection correction coefficient sequences that are within a predetermined range (the error is smaller than Lim) with respect to the registered non-ejection correction coefficient sequences can be combined into one, reducing the data amount. can do.

Next, a detailed example of unevenness correction processing using the index table (right adjacent non-discharge correction coefficient reference table, left adjacent non-discharge correction coefficient reference table) and non-discharge correction coefficient table created by the above method will be described.
FIG. 23 is a non-uniformity correction execution flowchart.

When this processing is started, first, the density unevenness correction coefficient table (COEF [Dmax] [Nnzl]), the non-ejection left adjacent correction coefficient reference table (L_TABLE [Nnzl]), and the non-ejection right adjacent correction coefficient reference table (R_TABLE [ Nnzl]) and the non-ejection correction coefficient table (T_COEF [Dmax] [Tmax]) are read (step S211).
Next, the actually measured non-discharge information (NPN [Nnzl]) is read (step S212). Here, as described above, the measurement non-ejection information is recorded as a test pattern in which a straight line is formed for each nozzle, detects whether or not a straight line corresponding to each nozzle is formed, and detects a non-ejection nozzle. Can be created. The measurement non-ejection information is information that the non-ejection nozzle is turned on and the normal nozzle (nozzle that ejects ink droplets) is turned off.
Next, unevenness / non-ejection selection information (F_npn []) for selecting a table corresponding to each nozzle is created based on the read measurement non-ejection information (step S214).
Specifically, when the left and right nozzles of the target nozzle (nzl) are normal nozzles (NPN [nzl + 1] = OFF and NPN [nzl-1] = OFF), F_npn [nzl] = 0 is set, and the target nozzle When (nzl) is a non-ejection nozzle, F_npn [nzl] = 1, and when the right nozzle of the target nozzle (nzl) is non-ejection (NPN [nzl + 1] = ON), F_npn [nzl] = 2 When the right nozzle of the target nozzle (nzl) is not ejecting (NPN [nzl-1] = ON), F_npn [nzl] = 3.

Then, the process of step S230 below is repeated for the entire range while sequentially changing the position (y value) to be calculated in the height direction (y direction) of the image (step S220).
That is, in step S230, a position to be calculated (value of x) is determined for the image width direction (x direction) in the y value related to the calculation target, and a nozzle number (nzl number) corresponding to the x position is determined for this x position. The unevenness correction coefficient and the non-ejection correction coefficient corresponding to the pixel density d [x] [y] and the nzl value are obtained from the density-specific unevenness correction coefficient table, the non-ejection left adjacent correction coefficient table, and the non-ejection right adjacent correction coefficient table. (Step S233).
When F_npn [nzl] = 0, the corresponding unevenness correction coefficients of nzl and image density d are read from the unevenness correction coefficient table for each density (COEF [d] [nzl]), and the read unevenness correction coefficient is used as the correction coefficient (f ).
When F_npn [nzl] = 1, the correction coefficient (f) is set to a predetermined constant (for example, 0).
When F_npn [nzl] = 2, the table number (t) is read from the corresponding nzl from the non-ejection left neighbor correction coefficient reference table (L_TABLE [Nnzl]), and the non-ejection correction coefficient table (T_COEF [Dmax] [Tmax] ) Read out the table number (t) and the unevenness correction coefficient (T_COEF [d] [t]) corresponding to the pixel density [d]. The read non-ejection correction coefficient (unevenness correction coefficient) is set as a correction coefficient (f).
When F_npn [nzl] = 3, the table number (t) is read from the corresponding nzl from the non-ejection left neighbor correction coefficient reference table (R_TABLE [Nnzl]), and the non-ejection correction coefficient table (T_COEF [Dmax] [Tmax] ) Read out the table number (t) and the unevenness correction coefficient (T_COEF [d] [t]) corresponding to the pixel density [d]. The read non-ejection correction coefficient (unevenness correction coefficient) is set as a correction coefficient (f).
Then, using this correction coefficient (f), the correction calculation is executed according to the above [Equation 16] (step S234).

Regarding the image width (x direction), steps S232 to S234 are repeated for the entire range of the image width while sequentially changing the position of x (step S230).
When the above correction calculation is completed for all image positions [x] [y], this process ends.
When a non-ejection correction coefficient sequence common to the index table and the plurality of nozzles is used, unevenness correction can be performed by performing the processing as described above.

Further, in the above embodiment, only the landing position error of each ejection unit is used as a recording characteristic, and the variation of dots formed by each recording element is not taken into consideration, but the present invention is not limited to this, and each ejection unit The droplet ejection diameter (amount of droplet ejection liquid) formed by the above may be calculated, and the variation in the diameter of the droplet ejection point formed at each discharge unit may be taken into account. In this way, the amount of overlap can be detected more accurately by taking into account the variation in the amount of droplet ejection between the droplet ejection points formed by the discharge section, and the image can be reproduced more accurately.
In addition, the diameter of the droplet ejection point formed in each discharge unit is, for example, as described in JP-A-2006-264069, by detecting the density profile of each straight line and detecting the width of the straight line. Can be calculated.

  Further, the calculation of the density correction coefficient based on the landing position error is preferably performed by all the discharge units, but the present invention is not limited to this, and only the discharge unit having a landing position deviation of a certain level or more is used as the correction target discharge unit. Only density unevenness due to recording characteristics such as landing position error of the discharge unit may be corrected.

  In the above embodiment, the correction coefficient calculation unit calculates the density unevenness correction coefficient and the non-ejection correction coefficient. However, the calculation unit that calculates the density unevenness correction coefficient and the calculation unit that calculates the non-ejection correction coefficient are different. It is good also as a calculation part. The same applies to the storage unit.

In this embodiment, four straight lines are formed as the test pattern. However, the present invention is not limited to this, and even if the straight lines are divided into two, the straight lines are divided into three. Even if it forms, it may divide into five or more and may form a straight line.
In the above-described embodiment, a straight line is used, but the landing position may be detected based on one droplet ejection point.

In addition, if the adjacent droplet ejection points are not in contact with each other on the recording medium, that is, if the droplet ejection point and the adjacent droplet ejection point are not in contact with each other, the droplet ejection points formed by all the ejection units are You may form on the same straight line in the direction perpendicular | vertical to a conveyance direction.
For example, when the size of the ejected ink droplet can be adjusted, that is, when the size of the droplet ejection point can be adjusted, the droplet ejection point can be reduced by reducing the ejected ink droplet and reducing the droplet ejection point. You may make it not contact an adjacent droplet ejection point.
As described above, by not contacting the droplet ejection point adjacent to the droplet ejection point, both ends of each droplet ejection point in the reference direction can be accurately calculated.

  In the present embodiment, the ink discharge data refinement unit generates the discharge control signal by converting the image data into multiple values (5-value, that is, not forming four types of droplet ejection points and droplet ejection points). The present invention is not limited to this, and the N value (N ≧ 2) may be set in accordance with the ejection performance of the recording head. For example, when the recording head can eject large dots and small dots, the image data may be subjected to ternarization processing in order to generate an ejection control signal composed of three values: large dots, small dots, and no ejection. Alternatively, binarization may be performed to discharge or not discharge.

  In the above-described embodiment, the recording head of the drawing unit is a full-line head type in which the ejection units are arranged in a line, but the recording head is not limited to a single-row arrangement, and as shown in FIG. 50′K may be arranged in a staggered manner by shifting the plurality of rows of ejection portions by a fixed pitch. In this manner, by arranging the ejection units 60 in a staggered manner and forming one row of droplet ejection points with a plurality of rows of ejection units, it is possible to form an image with higher resolution.

In this embodiment, the recording head unit has a standard YMCK color (four colors) configuration, but the combination of ink colors and the number of colors is not limited to this embodiment. For example, light ink and dark ink are used. May be added. More specifically, it is possible to add a recording head that discharges light ink such as light cyan and light magenta.
Further, the recording head unit can be used only as a recording head that discharges K (black) ink, that is, a monochrome recording head unit, and can be used as an image drawing apparatus that draws a monochrome image.

  As described above, the image recording method and the image recording apparatus according to the present invention have been described in detail. However, the present invention is not limited to the above embodiments, and various improvements and modifications can be made without departing from the gist of the present invention. Changes may be made.

  For example, in the above-described image recording apparatus, a thermosetting ink is used as the ink, and the ink landed on the recording medium by the heating and pressing unit is fixed on the recording medium. However, the present invention is not limited to this. Various inks can be used. For example, when using a photocurable ink as the ink, a light irradiation mechanism is provided as a fixing unit, the active energy curable ink is ejected from the recording head, and an image of the photocurable ink is formed on the recording medium P. Thereafter, an active light beam is irradiated to cure the image and fix the image on the recording medium. Here, when a UV curable ink is used as the photocurable ink, various ultraviolet light sources such as a metal halide lamp, a high-pressure mercury lamp, and a UVLED may be used as the fixing unit.

  In the present embodiment, the image recording apparatus has been described. However, the present invention is not limited to this, and will be described in detail later along with a specific example. For example, an image recorded on the recording medium P is heated and added. An image recording apparatus that fixes the image on the recording medium P by pressing can also be used.

Hereinafter, the calculation method of the density correction coefficient based on the landing position error will be described more specifically.
In the following, it is assumed that the density correction coefficient p [i] is di and the landing position error a [i] is xi.

  As described above, the density correction coefficient di for the landing position error of a specific nozzle is determined by the following equation.

ここで、ｘｉはそれぞれ補正対象ノズルの理想着弾位置を原点とした各ノズルの着弾位置である。Πは、補正に用いるＮ本のノズル内で積をとることを意味する。Ｎ＝３の場合について明示的に表すと、次のようになる。

Here, xi is the landing position of each nozzle with the ideal landing position of the correction target nozzle as the origin. Π means taking a product in N nozzles used for correction. The case of N = 3 is expressed explicitly as follows.

  From the condition of minimizing the low frequency component of the power spectrum of density unevenness, the density correction coefficient of each nozzle can be theoretically derived.

  First, a density profile that incorporates error characteristics of each nozzle (that is, the discharge section) is defined as follows.

画像の濃度プロファイルＤ(x)は、各ノズルが印字する濃度プロファイルの和であり、ノズルの印字を表すのが印字モデル（１ノズルが印字する濃度プロファイル）である。印字モデルはノズル出力濃度Ｄｉと標準濃度プロファイルｚ(x)に分離して表現される。

The density profile D (x) of the image is the sum of the density profiles printed by each nozzle, and the printing model (density profile printed by one nozzle) represents the printing of the nozzles. The print model is expressed separately as a nozzle output density Di and a standard density profile z (x).

  Strictly speaking, the standard density profile z (x) has a finite spread equal to the dot diameter, but considering the correction of the position error as a problem of density deviation balancing, what is important is the position of the center of gravity of the density profile. The (landing position) and the spread of the density profile is a secondary factor. Therefore, an approximation that replaces the profile with a δ function is reasonable. Assuming such a standard concentration profile, mathematical handling becomes easy and an exact solution of the correction coefficient is obtained.

  When the profile is approximated by a δ function model, the standard concentration profile is expressed by the following equation.

補正係数を導出するにあたり、ある特定のノズル（ｉ＝０）の着弾位置誤差Δｘ０を、周辺ノズルＮ本によって補正することを考える。なお、ここでは補正対象ノズルの番号をｉ＝０とした。また、周辺のノズルも、所定の着弾位置誤差を持ち得ることに注意する。

In deriving the correction coefficient, it is considered that the landing position error Δx0 of a specific nozzle (i = 0) is corrected by N peripheral nozzles. Here, the correction target nozzle number is i = 0. Note that peripheral nozzles can also have a predetermined landing position error.

The number (index) of the N nozzles including the correction target nozzle (center nozzle) is expressed by the following equation.

なお、この式においては、Ｎは奇数である必要があるが、本発明の実施に際しては、Ｎを奇数に限定する必要はない。

In this equation, N needs to be an odd number, but it is not necessary to limit N to an odd number when implementing the present invention.

  The initial output density (output density before correction) is expressed by the following equation assuming that only i = 0 has a value.

濃度補正係数をｄｉとするとき、補正後出力濃度Ｄｉ’は、次式で表される。

When the density correction coefficient is di, the corrected output density Di ′ is expressed by the following equation.

つまり、ｉ＝０では初期出力濃度値と補正値（ｄｉ×Ｄｉｎｉ）の和で表され、ｉ≠０では補正値のみとなる。

That is, when i = 0, it is represented by the sum of the initial output density value and the correction value (di × Dini), and when i ≠ 0, only the correction value is obtained.

  The landing position xi of each nozzle i is expressed by the following equation.

δ関数型印字モデルを用いると、補正後の濃度プロファイルは、次式で表される。

When the δ function type printing model is used, the corrected density profile is expressed by the following equation.

これに対してFourier変換を行うと、次式、

On the other hand, when performing Fourier transform,

と表される。なお、Ｄｉｎｉは共通の定数のため省略した。

It is expressed. Dini is omitted because it is a common constant.

  Minimizing the visibility of density unevenness is to minimize the low frequency component of the power spectrum of the following equation.

これは、数学的にはＴ(f)の f＝０における微分係数（１次、２次、…）がゼロである
ことで近似できる。今、未知数ｄｉ’はＮ個であるから、ＤＣ成分の保存条件も含めると、Ｎ−１次までの微分係数がゼロの条件を用いれば、全ての（Ｎ個の）未知数ｄｉ’が厳密に定まる。このようにして、以下の補正条件が定まる。

This can be mathematically approximated by the fact that the differential coefficient (first order, second order,...) Of T (f) at f = 0 is zero. Since the number of unknowns di ′ is now N, if the condition for storing the DC component is included, all (N) unknowns di ′ are strictly determined by using the condition that the differential coefficients up to the N−1 order are zero. Determined. In this way, the following correction conditions are determined.

δ関数モデルにおいては、各補正条件を展開していくと、容易な計算によってＤｉについてのＮ本の連立方程式に帰着する。各補正条件を展開したものを整理すると、以下の条件群（方程式群）が得られる。

In the δ function model, when each correction condition is developed, it is reduced to N simultaneous equations for Di by easy calculation. Arranging the development of each correction condition gives the following condition group (equation group).

これらの方程式群の意味するところは、１式目はＤＣ成分の保存であり、２式目は重心位置の保存を表している。３式目以降は統計学におけるＮ−１次モーメントがゼロであることを表している。

The meaning of these equations is that the first equation represents preservation of the DC component, and the second equation represents preservation of the center of gravity. The third and subsequent formulas indicate that the N-1th moment in statistics is zero.

  When the conditional expression thus obtained is expressed in matrix form, it can be expressed as follows.

この係数行列Ａは、いわゆるVander monde型の行列であり、その行列式は差積を用いて次式となることが知られている。

The coefficient matrix A is a so-called Vander monde type matrix, and it is known that the determinant is expressed by the following equation using a difference product.

このため、Crammerの公式を用いてｄｉ’の厳密解を求めることができる。計算の詳細な過程は省略するが、代数計算によって、その解は次式となることが示される。

For this reason, the exact solution of di ′ can be obtained using Cramer's formula. The detailed process of the calculation is omitted, but the algebraic calculation shows that the solution is

よって、求めるべき補正係数ｄｉは、次式となる。

Therefore, the correction coefficient di to be obtained is as follows.

以上のように、パワースペクトルの原点微分係数をゼロにするという条件から、濃度補正係数ｄｉの厳密解が導かれる。補正に用いる周辺ノズル数Ｎを増やすほど、より高次の
微分係数をゼロにすることが可能になるため、低周波エネルギーがより小さくなり、ムラの視認性は一層低減する。

As described above, the exact solution of the density correction coefficient di is derived from the condition that the origin derivative coefficient of the power spectrum is zero. As the number N of peripheral nozzles used for correction is increased, the higher-order differential coefficient can be made zero, so that the low frequency energy becomes smaller and the visibility of unevenness is further reduced.

  In this embodiment, the condition for setting the origin differential coefficient to zero is used, but even if it is not completely zero, it is set to a sufficiently small value (for example, 1/10 before correction) compared to the differential coefficient before correction. However, the low frequency component of the power spectrum of density unevenness can be made sufficiently small. That is, in terms of the condition that the low frequency component of the power spectrum is reduced to such an extent that density unevenness is not visually recognized, the range of the value is set in the sense that the origin differential coefficient of the power spectrum is set to a sufficiently small value (approximately 0). To 1/10 or less of the absolute value of the differential coefficient before correction.

  In consideration of human visual characteristics, the visibility of density unevenness is in a low frequency region of 0 to 8 cycles / mm, and the smaller the power spectrum in this region, the higher the correction accuracy.

  If the density correction coefficient of the nozzle i with respect to the position error of the nozzle k is d (i, k), this d (i, k) can be obtained by the equation [Equation 16]. Then, the total density correction coefficient di of the nozzle i is obtained as the following equation.

なお、上記の例では、全ノズルの着弾位置誤差を補正対象としてインデックスｋを足し合わせているが、ある値ΔＸ＿ｔｈｒｅｓｈを閾値として予め設定しておき、この閾値を超える着弾位置誤差をもつノズルのみを補正対象とするように選択的に補正する構成も可能である。

In the above example, the index k is added with the landing position errors of all nozzles as correction targets. However, a certain value ΔX_thresh is set in advance as a threshold value, and only nozzles having landing position errors exceeding this threshold value are set. A configuration in which correction is selectively performed so as to be a correction target is also possible.

  As described above, when the number N of nozzles used for correction is increased, the correction accuracy is improved. However, the change width of the density correction coefficient is also increased, and there is a possibility that the reproduced image is broken. Therefore, a correction coefficient limit range (upper limit value d_max and lower limit value d_min) for preventing image corruption is determined, and N is set so that the total density correction coefficient obtained by the above equation [23] falls within the limit range. It is desirable to set a value. That is, the N value is determined so as to satisfy d_min <di <d_max.

According to experimental knowledge, image failure does not occur if d_min ≧ −1 and d_max ≦ 1 are satisfied.

It is a front view which shows schematic structure of an image recording device. FIG. 2 is a top view showing a suction conveyance bell and a recording head unit of the image recording apparatus shown in FIG. 1. (A) is a front view showing an arrangement pattern of ejection portions of the recording head, and (B) is an enlarged sectional view showing one ejection portion of the recording head shown in (A). FIG. 3 is a schematic diagram illustrating a configuration of an ink supply system and a head peripheral portion in the image recording apparatus. It is a principal block diagram which shows the system configuration | structure of the control part shown in FIG. It is a flowchart which shows each process of image recording. (A) is a schematic diagram which shows an example of a test pattern, (B) is the elements on larger scale of (A). It is a flowchart which shows the example of calculation of a density | concentration correction | amendment / non-discharge correction coefficient. It is a flowchart which shows the example of calculation of a density | concentration correction | amendment / non-discharge correction coefficient. It is a graph which shows the relationship between an image density and a Todd droplet ejection rate. It is a graph which shows the relationship between a droplet ejection kind and a liquid quantity. It is a flowchart which shows the flow of a process of image data. It is a nonuniformity correction execution flowchart. It is a flowchart of the error diffusion method implemented in N-value conversion processing. It is explanatory drawing which shows an example of a data storage cell. It is explanatory drawing for demonstrating the process of N-value-izing process. It is explanatory drawing which shows the example of a threshold value table. It is a schematic diagram which shows an example of the spreading | diffusion method of an error value. It is explanatory drawing for demonstrating the process of N-value-izing process. FIG. 6 is an explanatory diagram conceptually illustrating an example of a relationship between a non-uniformity correction coefficient and a non-ejection correction coefficient, an image density, a nozzle position (number), and non-uniformity / non-ejection selection information in a control unit. It is explanatory drawing which shows notionally other examples of the relationship between the unevenness correction coefficient in a control part, a non-ejection correction coefficient, an image density, a nozzle position (number), and nonuniformity / non-ejection selection information. It is a flowchart which shows the preparation method of the non-ejection correction LUT. It is a nonuniformity correction execution flowchart. It is an illumination figure which shows another example of the arrangement pattern of the discharge part of a recording head.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Image recording device 12 Supply part 14 Conveying part 16 Drawing part 18 Heating and pressurizing part 20 Discharge part 22 Control part 24 Scanner 30 Magazine 32 Heating drum 34, 56 Cutter 34A, 56A Fixed blade 34B, 56B Round blade 36 Adsorption belt conveyance part 38 Belt 39 Adsorption chamber 40 Fan 42 Belt cleaning unit 44 Heating fan 46 Post-drying unit 50 Recording head unit 50K, 50C, 50M, 50Y Recording head (inkjet head)
52 Ink Storage / Loading Unit 54 Pressure Roller 58 Ejection Unit 60 Ejection Unit 61 Ink Chamber Unit 62 Nozzle 63 Pressure Chamber 64 Supply Port 65 Common Channel 66 Actuator 67 Pressure Plate 68 Individual Electrode 70 Ink Supply Tank 72 Filter 74 Cap 76 Cleaning Blade 77 Suction pump 78 Collection tank 80 Communication interface 82 System controller 84 Image memory 86 Motor driver 88 Heat driver 90 Print controller 92 Image buffer memory 94 Head driver 96 Host computer 98 Motor 99 Heater P Recording medium

Claims (7)

A recording head having a plurality of recording elements for discharging ink droplets;
Conveying means for conveying at least one of the recording head and the recording medium to relatively move the recording head and the recording medium;
Unevenness correction coefficient calculation storage means for storing unevenness correction coefficient values calculated for each pixel density based on unevenness information for each recording element read in advance with a test pattern as one of the recording characteristics of the recording element;
For all recording elements each in advance based on the test concentration information of each recording element read by the pattern, assuming a case where the recording element in the vicinity of each of the recording elements becomes non-discharge, image density every operation A non-ejection correction coefficient calculation storage means for storing the non-ejection correction coefficient value as one of the recording characteristics;
Non-ejection information detecting means for detecting non-ejection information of the recording element;
Based on the pixel density and the non-ejection information of each recording element, the recording characteristics of the recording elements in the vicinity of the non-ejection recording element indicated by the non -ejection information are calculated from the unevenness correction coefficient calculation storage means and the non-ejection correction coefficient calculation storage means. A selection means to select;
Correction processing means for correcting the pixel density of the density signal based on the recording characteristics selected by the selection means;
An image recording apparatus comprising: drive control means for controlling drive of the recording element based on the output density corrected by the correction processing means.   The image recording apparatus according to claim 1, wherein the non-ejection correction coefficient calculation storage unit calculates and stores a non-ejection correction coefficient value for each position with respect to the non-ejection nozzle. The ejection failure correction coefficient calculation storage means, an index to associate a lookup table for storing a plurality of ejection failure correction coefficient value, and a non-ejection correction coefficient value of each recording element and a look-up table for each position for non-ejection nozzle With table,
The index table, the recording element of the ejection failure correction coefficient value within a certain range of the ejection failure correction coefficient values stored in a look-up table, the image recording according to claim 1, associated with the ejection failure correction coefficient value apparatus. The unevenness correction coefficient calculation storage means, wherein the benzalkonium to determine the non-uniformity correction coefficient value Kiki recording element before based on the correction condition for reducing the low-frequency component of the power spectrum representing spatial frequency characteristic of the density unevenness The image recording apparatus according to claim 1.   The image recording apparatus according to claim 4, wherein the correction condition is a condition in which a differential coefficient at a frequency origin of a power spectrum representing a spatial frequency characteristic of density unevenness is substantially zero.   6. The correction condition is represented by N simultaneous equations obtained from a condition for preserving a DC component of spatial frequency and a condition that a differential coefficient up to the N-1 order is substantially zero. Image recording device. A recording head having a plurality of recording elements that discharge ink droplets; and a transport unit that transports at least one of the recording head and the recording medium and relatively moves the recording head and the recording medium; An image recording method for forming an image on the recording medium by the recording head while relatively scanning the recording head and the recording medium by means,
A non-uniformity correction coefficient calculation storage step for storing the non-uniformity correction coefficient value calculated for each pixel density based on the non-uniformity information for each recording element read by the test pattern as one of the recording characteristics of the recording element;
For all recording elements each, based on the density information of each recording element read by the test pattern, assuming a case where the recording element in the vicinity of each of the recording elements becomes non-discharge was calculated for each image density A non-ejection correction coefficient calculation storing step for storing a non-ejection correction coefficient value as one of the recording characteristics;
A non-ejection information detection step of detecting non-ejection information of the recording element;
Recording in the vicinity of the non-ejection recording element indicated by the non-ejection information from the recording characteristics stored in the unevenness correction coefficient calculation memory step and the non-ejection correction coefficient calculation memory step according to the pixel density and non-ejection information of each recording element. A selection step for selecting the recording characteristics of the element;
A correction processing step of correcting the pixel density of the density signal based on the recording characteristics selected by the selection means;
An image recording method comprising: an image output step of controlling driving of the recording element based on the output density corrected in the correction processing step and outputting an image on the recording medium.

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